I have the stock tarp and the hex. I prefer the stock tarp in most cases. I've had it out in several rains and never had a problem. The stock tarp takes less pack space and is easier to stow.

The hex gives more coverage and more ground space, but with my Ultralight it also increases the minimum distance feasible between trees to get a taut setup and cuts visibility from under the edge of the hammock and breezes to some extent. If I expect a lot of rain I sometimes take it. I used it on the AT last year in Georgia, but ended up wishing I had taken the stock tarp.

For the most part, the AT has shelters spaced so that you could use them if the weather were really horrible. Of course, given Murphy's Law, you may find yourself miles from a shelter when the storm hits...